1. Field of the Invention
This invention relates to building superstructures and, more particularly, to a novel and highly effective structural assembly and construction method for the rapid and inexpensive construction of lightweight building superstructures that are resistant to uplift, as from wind or inertial forces.
2. Description of the Prior Art
Among the leading disclosures of hollow metal log building construction are applicant's U.S. Pat. No. 4,619,089 for “Building Structure,” issued October 28, 1986, and U.S. Pat. No. 5,282,343, for “Building Structures, Elements and Methods for Constructing Same,” issued Feb. 1, 1994, and corresponding patents issued in other countries. The disclosures of the '089 and '343 patents identified above are incorporated herein by reference. The structures and methods developed by the applicant are believed to be the current state of the art relevant to the present invention.
Structures made in the ways previously developed by the applicant are suited for any location but especially for remote sites, possibly off the power grid, in areas with less developed economies, where rapid and inexpensive construction of small- to medium-sized houses, schools, storage sheds, commercial and community buildings, government and private office buildings and similar structures is a priority. Applicant's inventions have found wide and growing acceptance by public and private interests in many countries around the world.
Wind uplift is a problem in small- to medium-sized building superstructures of various designs, particularly if, as is often the case, they have eaves that extend out beyond the supporting walls. To the extent that air pressure on the underside of the eaves exceeds the pressure on the topside, there is a net upward force that can blow part or all of the roof off the walls. Even in the absence of eaves, wind can produce a Bernoulli Effect causing air pressure above the roof of a building to be less than the air pressure within the building and generating a dangerous uplift.
The problem of wind uplift is especially severe in inexpensive superstructures made not of solid wood or other heavy material but of sheet metal rolled into hollow metal “logs.” Such logs can be shipped inexpensively to a building construction site as flat sheets and formed into hollow logs onsite. But since superstructures comprising hollow metal logs are lightweight compared to most other designs, they are especially susceptible to wind uplift.
Indeed, the logs of such buildings are so light that, without suitable tie-downs, individual logs in a wall or even entire walls can be detached and blown away with the roof by winds of considerably less than hurricane force.
Inertial forces, as from earthquakes, can also generate uplift. If the ground under a building alternately rises and falls, conservation of momentum (initially zero relative to the earth) can cause the building to experience an upwardly directed inertial force that tends to separate the superstructure from the foundation, upper parts of walls from lower parts, or the roof from the walls.
In superstructures made of hollow metal logs, the problem of uplift due to whatever natural cause is conventionally addressed by attaching metal rods to the building foundation at building corners. Each rod extends vertically through connectors that connect horizontally extending adjacent logs forming the walls of the superstructure. The rods run the full height of the walls and are connected at their tops to the roof to serve as tie-downs.
Of course, this solution involves incremental costs of time and labor, which it is desirable to avoid. Of greater concern, workers who are poorly trained or inadequately supervised may omit the installation of the metal rods. Since the rods are not visible in the finished construction, the omission may go unnoticed until a high wind, an earthquake, or another cause of uplift damages or destroys the building.